I’ve been consulting with a client who has a wildly successful web-based system, with well over 10 million users and looking at a tenfold growth in the near future. One of the recent features in their system was to show users their local weather and it almost maxed out their capacity. That raised certain warning flags as to the ability of their current architecture to scale to the levels that the business was taking them.

On Web 2.0 Mashups

One would think that sites like Weather.com and friends would be the first choice for implementing such a feature. Only thing is that they were strongly against being mashed-up Web 2.0 style on the client – they had enough scalability problems of their own. Interestingly enough (or not), these partners were quite happy to publish their weather data to us and let us handle the whole scalability issue.

Implementation 1.0

The current implementation was fairly straightforward – client issues a regular web service request to the GetWeather webmethod, the server uses the user’s IP address to find out their location, then use that location to find the weather for that location in the database, and return that to the user. Standard fare for most dynamic data and the way most everybody would tell you to do it.

Only thing is that it scales like a dog.

Add Some Caching

The first thing you do when you have scalability problems and the database is the bottleneck is to cache, well, that’s what everybody says (same everybody as above).

The thing is that holding all the weather of the entire globe in memory, well, takes a lot of memory. More than is reasonable. In which case, there’s a fairly decent chance that a given request can’t be served from the cache, resulting in a query to the database, an update to the cache, which bumps out something else, in short, not a very good hit rate.

Not much bang for the buck.

If you have a single datacenter, having a caching tier that stores this data is possible, but costly. If you want a highly available, business continuity supportable, multi-datacenter infrastructure, the costs add up quite a bit quicker – to the point of not being cost effective (”You need HOW much money for weather?! We’ve got dozens more features like that in the pipe!”)

What we can do is to tell the client we’re responding to that they can cache the result, but that isn’t close to being enough for us to scale.

Look at the Data, Leverage the Internet

When you find yourself in this sort of situation, there’s really only one thing to do:

In order to save on bandwidth, the most precious commodity of the internet, the various ISPs and backbone providers cache aggressively. In fact, HTTP is designed exactly for that.

If user A asks for some html page, the various intermediaries between his browser and the server hosting that page will cache that page (based on HTTP headers). When user B asks for that same page, and their request goes through one of the intermediaries that user A’s request went through, that intermediary will serve back its cached copy of the page rather than calling the hosting server.

Also, users located in the same geographic region by and large go through the same intermediaries when calling a remote site.

Leverage the Internet

The internet is the biggest, most scalable data serving infrastructure that mankind was lucky enough to have happen to it. However, in order to leverage it – you need to understand your data and how your users use it, and finally align yourself with the way the internet works.

Let’s say we have 1,000 users in London. All of them are going to have the same weather. If all these users come to our site in the period of a few hours and ask for the weather, they all are going to get the exact same data. The thing is that the response semantics of the GetWeather webmethod must prevent intermediaries from caching so that users in Dublin and Glasgow don’t get London weather (although at times I bet they’d like to).

REST Helps You Leverage the Internet

Rather than thinking of getting the weather as an operation/webmethod, we can represent the various locations weather data as explicit web resources, each with its own URI. Thus, the weather in London would be http://weather.myclient.com/UK/London.

If we were able to make our clients in London perform an HTTP GET on http://weather.myclient.com/UK/London then we could return headers in the HTTP response telling the intermediaries that they can cache the response for an hour, or however long we want.

That way, after the first user in London gets the weather from our servers, all the other 999 users will be getting the same data served to them from one of the intermediaries. Instead of getting hammered by millions of requests a day, the internet would shoulder easily 90% of that load making it much easier to scale. Thanks Al.

This isn’t a “cheap trick”. While being straight forward for something like weather, understanding the nature of your data and intelligently mapping that to a URI space is critical to building a scalable system, and reaping the benefits of REST.

What’s left?

The only thing that’s left is to get the client to know which URI to call. A simple matter, really.

When the user logs in, we perform the IP to location lookup and then write a cookie to the client with their location (UK/London). That cookie then stays with the user saving us from having to perform that IP to location lookup all the time. On subsequent logins, if the cookie is already there, we don’t do the lookup.

BTW, we also show the user “you’re in London, aren’t you?” with the link allowing the user to change their location, which we then update the cookie with and change the URI we get the weather from.

In Closing

While web services are great for getting a system up and running quickly and interoperably, scalability often suffers. Not so much as to be in your face, but after you’ve gone quite a ways and invested a fair amount of development in it, you find it standing between you and the scalability you seek.

Moving to REST is not about turning on the “make it restful” switch in your technology stack (ASP.NET MVC and WCF, I’m talking to you). Just like with databases there is no “make it go fast” switch – you really do need to understand your data, the various users access patterns, and the volatility of the data so that you can map it to the “right” resources and URIs.

If you do walk the RESTful path, you’ll find that the scalability that was once so distant is now within your grasp.

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Hi Udi,
when I read article I was wandering whether there is possibility to do solution with slightly different approach.

Let assume following:
1) You will group weather data from several cities into logical groups (i.e. in GB you might do that according administrative regions – South West England, West Midlands, Yorkshire and the Humber, etc. For example Czech Republic as small country might be represented by only one logical group while USA might get logical groups according counties or metro regions, etc.).

2) Single logical group contains weather data for several cities – like South West England has data for Plymouth, Bristol, Gloucester, etc.).

3) User location is identified on its login as you have described above and saved via cookie. Location definition is additionally extended with identification of region (or logical group for that matter) under which user belongs (i.e. user from Bristol will get not only cookie for Bristol but also region “South West England” maybe via some index/ID). This ID is saved into cookie as well.

4) When weather data are requested then provider site send out weather data for entire region via ID and not via specific city name. User presentation will than might select detail weather info in case city name is explicitly listed in delivered data or entire region if city/town/village is not available from list.

Logical group of weather data seems to me might then get into cashing tier inside datacenter (under assumption weather data are reasonably sized) as resource consumption shall not be that big if assumed 1) “(traditional) follow-the-sun/moon” user access pattern and 2) user base is usually not distributed evenly across all countries/regions but rather “packed” in certain distinct geo-locations. Moreover you are mentioned there is multiple datacenters and therefore each datacenter might server different user geo-location which shall farther decrease resource use.

I would appreciate if you can more elaborate on cases where is reasonable to use caching tier as opposite to cases where web cache infrastructure helps well (for example Facebook has more users then this application and they are using caching tier extensively quite happily).

I’m also wondering how you can cope with situation where all “web based caching” is “not working or is expired at the same time” and designed application must serve requests directly. Would not make sense to add some kind of cashing tier to the final application anyway? It does not seem the REST might help here.

[...] Building Super-Scalable Web Systems with REST – Udi Dahan talks about how REST services can help you to build the most highly scalable web systems, focusing on how the protocol provides a number of useful features that really help. Also well worth checking out are the caching documents mentioned in the first comment. [...]

On 1,2,3 and 4 – that’s actually how it’s being done. The blog post was an intentional simplification to get the idea across.

On your point “Facebook has more users then this application and they are using caching tier extensively quite happily”

Well, I guess it depends on what they’re using it for

When it comes to their graph analytics, yes, that’s all being done in memory. However, that’s their core business. Weather is not this company’s core business.

Also, in an “either-or” comparison, this kind of web caching costs much less than a caching tier. That’s not to say we’re in an “either-or” situation, we can do both. That way, we shed much of the load onto the web and have much less to deal with in our caching tier.

When “everything expires”, you still don’t have all of your users requesting at the same time. The result of serving the response to one user’s request will be cached after the previous expiry for the next set of users – it’s not an issue.

And thanks for your detailed comment. It’s always great hearing from you.

@Libor
On caching, the other option is to use Web caching within your own boundaries. If you’ve got layered resources then there’s no reason that you can’t use Web based caching of these more granular resources within your own boundaries.

Udi,
Very nice innovative approach. I like it.
My comment is however, that in doing what you are proposing the end user is the one that is ultimately going to suffer.

The moment you bring in caching (location + weather data) you immediately create potential problems in the user experience – a good example is the “are you not in Londong?” thing that is there to actually solve a user experience problem of a user NOT being where you think he is. There are of course many other potential problems where a solution is not as easy (wrong weather data etc..).

My question is: Since these potential problems are going to affect a very minor set of customers, lets say no more then 0.5% of the customers. However, as you begin with these methods because of scalability issues as you wrote, having 10 million customers or more would mean that at least 50,000 customers would get affected.

How would you weigh the benefit of the added scalability with the “cost” of customer issues for 50,000 unhappy customers or more for which you hurt their experience compared the the tradition “web method” approach?

I’ve found that when big numbers are involved, it’s important to get percentages accurate by measuring to understand the exact scope of any impact.

Next, we’re careful not to throw the baby out with the bath water. The business is the one that decides what’s worse, the extra expense of providing 100% of the users with always accurate data, or N users with degraded functionality. I have yet to see a business scaling to this many users choosing accuracy over profitability.

Finally, we look at ways to minimize the degradation of functionality – for instance, by comparing the user’s time zone with that of the location where we the cookie says they are. If there is a discrepancy, we refresh the location based on the current IP. This solves the problem for users travelling between time zones, further decreasing the number of affected users.

[...] Dahan, a big name in the field of building large scale web systems, shares some of his experiences with scaling a weather service. Although the lesson he learned might not apply to every other system out there, it provides a good [...]

This reinforces to me why SOA projects often ends up failing, because there is not enough emphasis on the data and how it can be partitioned. It also highlights why REST scales so well – caching and cache validation are built right into the protocol.

Did you add any of your own intermediaries for caching or was the intermediary caching happening as part of existing Intranet infrastructure?

I agree that a successful SOA requires a strong emphasis on the data. Too often when an organization is adopting SOAP – everything is through SOAP, and unfortunately SOAP does not carry the same caching and validation that REST does. In this case, a basic SOAP service would not take advantage of the infrastructure that is part of the Web and therefore could not scale as well as this REST solution. Further more, the nice thing about a solution like this, is that works equally well over the Internet or within an enterprise’s intranet.

The problem that I’ve found when “an organization is adopting SOAP”, is that it is purely technical change. While there may be some value in technical standardization, especially around application integration, no “quantum leaps” will come from it – definitely not IT Business alignment.

Only from asking the business about the semantics of their data and processes, and working with them in refining those models, can intelligent, business viable, technical decisions be made.

At that point, well, the right tool can be used for the right job – be that REST, SOAP, or flat files.

great article. It’s nice to see a real world example proving that REST, the architecture of the Web itself, can be implemented at the single-application level to circumvent show-stopping performance and scalability issues without the common “throw more hardware at it” resolution schema (a.k.a i’ll force you to spend TONS more money to try and band-aide the situation caused by my poor architecture choice)

Udi, great article. Some very cool stuff to think about. One thing I guess I don’t completely follow is relying on these Internet intermediaries you mentioned. Is it really that common for ISPs to offer that kind of caching just be “telling” them to do so via HTTP? Your description made me think more of content distribution networks like Akamai and such.

I did some poking around via Google to try to get a better understanding of who are the actual intermediaries you might have been referring to. I found a bunch of articles on the liabilities of being an intermediary instead. So, I’m still scratching my head a little bit. Perhaps, an article more on the specifics of making use of intermediaries? At any rate, keep writing!

Udi – quick question – this technique works wonders when the data is of a public nature, but what about sensitive data, like my account history at my banking site – what would you recommend there? Say my infrastructure is messaging using NSB – do I have a local cache on the web server (object DB, etc…) that’s being updated via pub-sub? Data at rest is a security liability, and I can’t keep the world in-memory for large sets of data such as account history…what to do?

Alright, so leaving banking aside – let’s say it’s email. I don’t want something to be able to do URL hacking and see everyone else’s messages by guessing unique URI’s – how do I prevent that? The data is encrypted on disk and only if the authenticated user which “owns” that data is accessing that URI will it be decrypted and sent over HTTPS? I’d worry about overloading the browser doing decrypt in javascript – is that actually performant? or secure for that matter?

HTTPS is used only to send the key.
At that point, data is sent over plain HTTP.
The data, however, is encrypted server side using that key before being sent over HTTP.
Then the browser decrypts the data using that key.

I don’t think you need to worry about performance problems on the browser – not unless you’re sending large quantities of data.

The question of how secure it is, well, that’s dependent on what assumptions you have of the user’s box. If it’s been root-kitted, all bets are off, regardless of how data gets to the user.

Security is not a boolean thing, it’s cost-benefit tradeoff just like everything else. Create a threat-model and assess solutions against it.

Interesting – I get it now – thanks for the clarification. So if I deliver the symmetric key during logon, let’s say, store it in a cookie (assuming current browser where CSRF attacks are mitigated) then subsequent requests can be done over HTTP and I don’t worry about URL hacking because the data is encrypted. I can do GET’s via AJAX to retrieve data, decrypt using the key in my cookie, and I’m able to take advantage of the fundamental caching behavior of the internet and browsers, assuming I have established correct expiry policy in my HTTP headers. Is that in line with what you’re proposing?

On security – yes – had a discussion the other day where the comment was “if the box is owned they could do IL injection or…” If the box is owned you’ve got MUCH bigger problems than IL injection, my friend.

Let me just add that you’re unlikely to achieve great performance improvements when using these patterns for private data at the single user level. While you can improve latency on subsequent requests by the same user for the same data (filtering/sorting done browser side), you won’t see the same level of throughput increases as with public data.

Certainly – I came around to the same conclusion after my last post – the real benefit of this approach is seen when the data is public. Thanks for your time on this – most appreciated – very interesting stuff.

We brought him on site to give our development staff the 5-day “Advanced Distributed System Design” training. The course profoundly changed our understanding and approach to SOA and distributed systems.

Consider some of the evidence: 1. Months later, developers still make allusions to concepts learned in the course nearly every day 2. One of our developers went home and made her husband (a developer at another company) sign up for the course at a subsequent date/venue 3. Based on what we learned, we’ve made constant improvements to our architecture that have helped us to adapt to our ever changing business domain at scale and speed If you have the opportunity to receive the training, you will make a substantial paradigm shift.

If I were to do the whole thing over again, I’d start the week by playing the clip from the Matrix where Morpheus offers Neo the choice between the red and blue pills. Once you make the intellectual leap, you’ll never look at distributed systems the same way.

Beyond the training, we were able to spend some time with Udi discussing issues unique to our business domain. Because Udi is a rare combination of a big picture thinker and a low level doer, he can quickly hone in on various issues and quickly make good (if not startling) recommendations to help solve tough technical issues.” November 11, 2010

Ian Robinson, Principal Consultant at ThoughtWorks
"Your blog and articles have been enormously useful in shaping, testing and refining my own approach to delivering on SOA initiatives over the last few years. Over and against a certain 3-layer-application-architecture-blown-out-to- distributed-proportions school of SOA, your writing, steers a far more valuable course."

Shy Cohen, Senior Program Manager at Microsoft
“Udi is a world renowned software architect and speaker. I met Udi at a conference that we were both speaking at, and immediately recognized his keen insight and razor-sharp intellect. Our shared passion for SOA and the advancement of its practice launched a discussion that lasted into the small hours of the night.It was evident through that discussion that Udi is one of the most knowledgeable people in the SOA space. It was also clear why – Udi does not settle for mediocrity, and seeks to fully understand (or define) the logic and principles behind things.Humble yet uncompromising, Udi is a pleasure to interact with.”

Glenn Block, Senior Program Manager - WCF at Microsoft
“I have known Udi for many years having attended his workshops and having several personal interactions including working with him when we were building our Composite Application Guidance in patterns & practices. What impresses me about Udi is his deep insight into how to address business problems through sound architecture. Backed by many years of building mission critical real world distributed systems it is no wonder that Udi is the best at what he does. When customers have deep issues with their system design, I point them Udi's way.”

Karl Wannenmacher, Senior Lead Expert at Frequentis AG
“I have been following Udi’s blog and podcasts since 2007. I’m convinced that he is one of the most knowledgeable and experienced people in the field of SOA, EDA and large scale systems.
Udi helped Frequentis to design a major subsystem of a large mission critical system with a nationwide deployment based on NServiceBus. It was impressive to see how he took the initial architecture and turned it upside down leading to a very flexible and scalable yet simple system without knowing the details of the business domain.
I highly recommend consulting with Udi when it comes to large scale mission critical systems in any domain.”

Simon Segal, Independent Consultant
“Udi is one of the outstanding software development minds in the world today, his vast insights into Service Oriented Architectures and Smart Clients in particular are indeed a rare commodity. Udi is also an exceptional teacher and can help lead teams to fall into the pit of success. I would recommend Udi to anyone considering some Architecural guidance and support in their next project.”

Ohad Israeli, Chief Architect at Hewlett-Packard, Indigo Division
“When you need a man to do the job Udi is your man! No matter if you are facing near deadline deadlock or at the early stages of your development, if you have a problem Udi is the one who will probably be able to solve it, with his large experience at the industry and his widely horizons of thinking , he is always full of just in place great architectural ideas.
I am honored to have Udi as a colleague and a friend (plus having his cell phone on my speed dial).”

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“Everyone will tell you how smart and knowledgable Udi is ... and they are oh-so-right. Let me add that Udi is a smart LISTENER. He's always calibrating what he has to offer with your needs and your experience ... looking for the fit. He has strongly held views ... and the ability to temper them with the nuances of the situation.I trust Udi to tell me what I need to hear, even if I don't want to hear it, ... in a way that I can hear it. That's a rare skill to go along with his command and intelligence.”

Eli Brin, Program Manager at RISCO Group
“We hired Udi as a SOA specialist for a large scale project. The development is outsourced to India. SOA is a buzzword used almost for anything today. We wanted to understand what SOA really is, and what is the meaning and practice to develop a SOA based system.
We identified Udi as the one that can put some sense and order in our minds. We started with a private customized SOA training for the entire team in Israel. After that I had several focused sessions regarding our architecture and design.
I will summarize it simply (as he is the software simplist): We are very happy to have Udi in our project. It has a great benefit. We feel good and assured with the knowledge and practice he brings. He doesn’t talk over our heads. We assimilated nServicebus as the ESB of the project. I highly recommend you to bring Udi into your project.”

Catherine Hole, Senior Project Manager at the Norwegian Health Network
“My colleagues and I have spent five interesting days with Udi - diving into the many aspects of SOA. Udi has shown impressive abilities of understanding organizational challenges, and has brought the business perspective into our way of looking at services. He has an excellent understanding of the many layers from business at the top to the technical infrstructure at the bottom. He is a great listener, and manages to simplify challenges in a way that is understandable both for developers and CEOs, and all the specialists in between.”

Yoel Arnon, MSMQ Expert
“Udi has a unique, in depth understanding of service oriented architecture and how it should be used in the real world, combined with excellent presentation skills. I think Udi should be a premier choice for a consultant or architect of distributed systems.”

Vadim Mesonzhnik, Development Project Lead at Polycom
“When we were faced with a task of creating a high performance server for a video-tele conferencing domain we decided to opt for a stateless cluster with SQL server approach. In order to confirm our decision we invited Udi.

After carefully listening for 2 hours he said: "With your kind of high availability and performance requirements you don’t want to go with stateless architecture."

One simple sentence saved us from implementing a wrong product and finding that out after years of development. No matter whether our former decisions were confirmed or altered, it gave us great confidence to move forward relying on the experience, industry best-practices and time-proven techniques that Udi shared with us.
It was a distinct pleasure and a unique opportunity to learn from someone who is among the best at what he does.”

I would strongly recommend this course to anyone with an interest in how to develop IT systems which provide immediate and future fitness for purpose. An influential and innovative thought leader and practitioner in his field, Udi demonstrates and shares a phenomenally in depth knowledge that proves his position as one of the premier experts in his field globally.

The course has enhanced my knowledge and skills in ways that I am able to immediately apply to provide benefits to my employer. Additionally though I will be able to build upon what I learned in my 2 days with Udi and have no doubt that it will only enhance my future career.

He accompanied us in all stages of our development cycle and helped us put vision into real life distributed scalable software. He brought fresh thinking, great in depth of understanding software, and ongoing support that proved as valuable and cost effective.

Udi has the unique ability to analyze the business problem and come up with a simple and elegant solution for the code and the business alike.With Udi's attention to details, and knowledge we avoided pit falls that would cost us dearly.”

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“Udi delivered a 5 hour long workshop on SOA for aspiring architects in Norway. While keeping everyone awake and excited Udi gave us some great insights and really delivered on making complex software challenges simple. Truly the software simplist.”

Motty Cohen, SW Manager at KorenTec Technologies
“I know Udi very well from our mutual work at KorenTec. During the analysis and design of a complex, distributed C4I system - where the basic concepts of NServiceBus start to emerge - I gained a lot of "Udi's hours" so I can surely say that he is a professional, skilled architect with fresh ideas and unique perspective for solving complex architecture challenges. His ideas, concepts and parts of the artifacts are the basis of several state-of-the-art C4I systems that I was involved in their architecture design.”

We’d been meaning to delve into messaging at Eleutian after multiple discussions with and blog posts from Greg Young and Udi Dahan in the past. We weren’t entirely sure where to start, how to start, what tools to use, how to use them, etc. Being able to sit in a room with Udi for an entire week while he described exactly how, why and what he does to tackle a massive enterprise system was invaluable to say the least.

We now have a much better direction and, more importantly, have the confidence we need to start introducing these powerful concepts into production at Eleutian.”

Gad Rosenthal, Department Manager at Retalix
“A thinking person. Brought fresh and valuable ideas that helped us in architecting our product. When recommending a solution he supports it with evidence and detail so you can successfully act based on it. Udi's support "comes on all levels" - As the solution architect through to the detailed class design. Trustworthy!”

Chris Bilson, Developer at Russell Investment Group
“I had the pleasure of attending a workshop Udi led at the Seattle ALT.NET conference in February 2009. I have been reading Udi's articles and listening to his podcasts for a long time and have always looked to him as a source of advice on software architecture.When I actually met him and talked to him I was even more impressed. Not only is Udi an extremely likable person, he's got that rare gift of being able to explain complex concepts and ideas in a way that is easy to understand.All the attendees of the workshop greatly appreciate the time he spent with us and the amazing insights into service oriented architecture he shared with us.”

Alexey Shestialtynov, Senior .Net Developer at Candidate Manager
“I met Udi at Candidate Manager where he was brought in part-time as a consultant to help the company make its flagship product more scalable. For me, even after 30 years in software development, working with Udi was a great learning experience. I simply love his fresh ideas and architecture insights.As we all know it is not enough to be armed with best tools and technologies to be successful in software - there is still human factor involved. When, as it happens, the project got in trouble, management asked Udi to step into a leadership role and bring it back on track. This he did in the span of a month. I can only wish that things had been done this way from the very beginning.I look forward to working with Udi again in the future.”

Christopher Bennage, President at Blue Spire Consulting, Inc.
“My company was hired to be the primary development team for a large scale and highly distributed application. Since these are not necessarily everyday requirements, we wanted to bring in some additional expertise. We chose Udi because of his blogging, podcasting, and speaking. We asked him to to review our architectural strategy as well as the overall viability of project.
I was very impressed, as Udi demonstrated a broad understanding of the sorts of problems we would face. His advice was honest and unbiased and very pragmatic. Whenever I questioned him on particular points, he was able to backup his opinion with real life examples.
I was also impressed with his clarity and precision. He was very careful to untangle the meaning of words that might be overloaded or otherwise confusing. While Udi's hourly rate may not be the cheapest, the ROI is undoubtedly a deal.
I would highly recommend consulting with Udi.”

Robert Lewkovich, Product / Development Manager at Eggs Overnight
“Udi's advice and consulting were a huge time saver for the project I'm responsible for. The $ spent were well worth it and provided me with a more complete understanding of nServiceBus and most importantly in helping make the correct architectural decisions earlier thereby reducing later, and more expensive, rework.”

The class was very well put together. The materials were clear and concise and Udi did a fantastic job presenting it. It was a good mixture of lecture, coding, and question and answer. I fully expected that I would be taking notes like crazy, but it was so well laid out that the only thing I wrote down the entire course was what I wanted for lunch. Udi provided us with all the lecture materials and everyone has access to all of the samples which are in the nServiceBus trunk.

Now I know why Udi is the "Software Simplist." I was amazed to find that all the code and solutions were indeed very simple. The patterns that Udi presented keep things simple by isolating complexity so that it doesn't creep into your day to day code. The domain code looks the same if it's running in a single process or if it's running in 100 processes.”

Ian Cooper, Team Lead at Beazley
“Udi is one of the leaders in the .Net development community, one of the truly smart guys who do not just get best architectural practice well enough to educate others but drives innovation. Udi consistently challenges my thinking in ways that make me better at what I do.”

Liron Levy, Team Leader at Rafael
“I've met Udi when I worked as a team leader in Rafael. One of the most senior managers there knew Udi because he was doing superb architecture job in another Rafael project and he recommended bringing him on board to help the project I was leading.Udi brought with him fresh solutions and invaluable deep architecture insights. He is an authority on SOA (service oriented architecture) and this was a tremendous help in our project.On the personal level - Udi is a great communicator and can persuade even the most difficult audiences (I was part of such an audience myself..) by bringing sound explanations that draw on his extensive knowledge in the software business. Working with Udi was a great learning experience for me, and I'll be happy to work with him again in the future.”

Adam Dymitruk, Director of IT at Apara Systems
“I met Udi for the first time at DevTeach in Montreal back in early 2007. While Udi is usually involved in SOA subjects, his knowledge spans all of a software development company's concerns. I would not hesitate to recommend Udi for any company that needs excellent leadership, mentoring, problem solving, application of patterns, implementation of methodologies and straight out solution development.There are very few people in the world that are as dedicated to their craft as Udi is to his. At ALT.NET Seattle, Udi explained many core ideas about SOA. The team that I brought with me found his workshop and other talks the highlight of the event and provided the most value to us and our organization. I am thrilled to have the opportunity to recommend him.”

Eytan Michaeli, CTO Korentec
“Udi was responsible for a major project in the company, and as a chief architect designed a complex multi server C4I system with many innovations and excellent performance.”

Carl Kenne, .Net Consultant at Dotway AB
“Udi's session "DDD in Enterprise apps" was truly an eye opener. Udi has a great ability to explain complex enterprise designs in a very comprehensive and inspiring way. I've seen several sessions on both DDD and SOA in the past, but Udi puts it in a completly new perspective and makes us understand what it's all really about. If you ever have a chance to see any of Udi's sessions in the future, take it!”

Avi Nehama, R&D Project Manager at Retalix
“Not only that Udi is a briliant software architecture consultant, he also has remarkable abilities to present complex ideas in a simple and concise manner, and... always with a smile. Udi is indeed a top-league professional!”

Ben Scheirman, Lead Developer at CenterPoint Energy
“Udi is one of those rare people who not only deeply understands SOA and domain driven design, but also eloquently conveys that in an easy to grasp way. He is patient, polite, and easy to talk to. I'm extremely glad I came to his workshop on SOA.”

Scott C. Reynolds, Director of Software Engineering at CBLPath
“Udi is consistently advancing the state of thought in software architecture, service orientation, and domain modeling.
His mastery of the technologies and techniques is second to none, but he pairs that with a singular ability to listen and communicate effectively with all parties, technical and non, to help people arrive at context-appropriate solutions.
Every time I have worked with Udi, or attended a talk of his, or just had a conversation with him I have come away from it enriched with new understanding about the ideas discussed.”

Rhys Campbell, Owner at Artemis West
“For many years I have been following the works of Udi. His explanation of often complex design and architectural concepts are so cleanly broken down that even the most junior of architects can begin to understand these concepts. These concepts however tend to typify the "real world" problems we face daily so even the most experienced software expert will find himself in an "Aha!" moment when following Udi teachings.
It was a pleasure to finally meet Udi in Seattle Alt.Net OpenSpaces 2008, where I was pleasantly surprised at how down-to-earth and approachable he was. His depth and breadth of software knowledge also became apparent when discussion with his peers quickly dove deep in to the problems we current face. If given the opportunity to work with or recommend Udi I would quickly take that chance. When I think .Net Architecture, I think Udi.”

Sverre Hundeide, Senior Consultant at Objectware
“Udi had been hired to present the third LEAP master class in Oslo. He is an well known international expert on enterprise software architecture and design, and is the author of the open source messaging framework nServiceBus.
The entire class was based on discussion and interaction with the audience, and the only Power Point slide used was the one showing the agenda.
He started out with sketching a naive traditional n-tier application (big ball of mud), and based on suggestions from the audience we explored different solutions which might improve the solution. Whatever suggestions we threw at him, he always had a thoroughly considered answer describing pros and cons with the suggested solution. He obviously has a lot of experience with real world enterprise SOA applications.”

Raphaël Wouters, Owner/Managing Partner at Medinternals
“I attended Udi's excellent course 'Advanced Distributed System Design with SOA and DDD' at Skillsmatter. Few people can truly claim such a high skill and expertise level, present it using a pragmatic, concrete no-nonsense approach and still stay reachable.”

Nimrod Peleg, Lab Engineer at Technion IIT
“One of the best programmers and software engineer I've ever met, creative, knows how to design and implemet, very collaborative and finally - the applications he designed implemeted work for many years without any problems!”

Jose Manuel Beas
“When I attended Udi's SOA Workshop, then it suddenly changed my view of what Service Oriented Architectures were all about. Udi explained complex concepts very clearly and created a very productive discussion environment where all the attendees could learn a lot. I strongly recommend hiring Udi.”

Daniel Jin, Senior Lead Developer at PJM Interconnection
“Udi is one of the top SOA guru in the .NET space. He is always eager to help others by sharing his knowledge and experiences. His blog articles often offer deep insights and is a invaluable resource. I highly recommend him.”

Pasi Taive, Chief Architect at Tieto
“I attended both of Udi's "UI Composition Key to SOA Success" and "DDD in Enterprise Apps" sessions and they were exceptionally good. I will definitely participate in his sessions again. Udi is a great presenter and has the ability to explain complex issues in a manner that everyone understands.”

Eran Sagi, Software Architect at HP
“So far, I heard about Service Oriented architecture all over.
Everyone mentions it – the big buzz word.
But, when I actually asked someone for what does it really mean, no one managed to give me a complete satisfied answer.
Finally in his excellent course “Advanced Distributed Systems”, I got the answers I was looking for.
Udi went over the different motivations (principles) of Services Oriented, explained them well one by one, and showed how each one could be technically addressed using NService bus.
In his course, Udi also explain the way of thinking when coming to design a Service Oriented system.
What are the questions you need to ask yourself in order to shape your system, place the logic in the right places for best Service Oriented system.

I would recommend this course for any architect or developer who deals with distributed system, but not only.
In my work we do not have a real distributed system, but one PC which host both the UI application and the different services inside, all communicating via WCF.
I found that many of the architecture principles and motivations of SOA apply for our system as well. Enough that you have SW partitioned into components and most of the principles becomes relevant to you as well.
Bottom line – an excellent course recommended to any SW Architect, or any developer dealing with distributed system.”